The I, IV, and V chords are called, respectively, the tonic, subdominant, and dominant chords.
The I IV and V chords are generally arranged (in the context of this node) in cadences, made up of two (or more) chords.
V-I is a perfect cadence, and is generally considered to have a "closed" sound. Many songs end with either this cadence or a plagal cadence.
IV-I is an plagal cadence, and is generally considered to have a "closed" sound, but not as strong as the perfect cadence.
IV-V is an imperfect cadence, and is generally considered to have an "open" or unfinished sound. (Some consider I-V as an imperfect cadence too).
See also: degrees of the scale